Chromium- and phosphate-free coating for electrically insulating an electric strip

Patent metadata

Field	Value
Publication number	US-11873408-B2
Application number	US-202016893738-A
Country	US
Kind code	B2
Filing date	Jun 5, 2020
Priority date	Dec 7, 2017
Publication date	Jan 16, 2024
Grant date	Jan 16, 2024

Abstract

The present invention relates to a method for providing electrically insulating and anti-corrosive coatings on electrical steel strip by using a phosphate-free aqueous dispersion. Furthermore, the invention relates to such an aqueous dispersion which is particularly suitable for providing electrically insulating and anti-corrosive coatings on electrical steel strip. The aqueous dispersion of the present invention is substantially free of phosphates and organic compounds and comprises silicates dissolved in water as an inorganic binder which forms the coating, and a mixture of oxide pigments of the elements titanium and aluminum. The subject matter of the invention also comprises a laminated electrical steel strip which is made from the electrical steel strip produced in the method according to the invention or from electrical steel strip coated with an aqueous dispersion according to the invention.

First claim

The invention claimed is:

1. A method for coating an electrical steel strip, comprising steps of:
applying a wet film of an aqueous chromium- and phosphate-free composition to at least a part of a surface of the electrical steel strip, which composition comprises:
A) at least 15 wt. % of silicates dissolved in water, calculated as SiO 2 ;
B) at least 4 wt. % of sodium and/or potassium ions dissolved in water, wherein a total content of the ions dissolved in water is calculated respectively as Na and/or K; and
C) at least 1 wt. % of at least one water-insoluble oxide pigment; and

drying the wet film on the surface of the electrical steel strip.

2. The method according to claim 1 , wherein the aqueous chromium- and phosphate-free composition contains, as component B), either:
i) only sodium ions or only potassium ions; or
ii) sodium and potassium ions, the amount ratio by mass Na:K being either greater than 10:1 or less than 1:10.

3. The method according to claim 2 , wherein the aqueous chromium- and phosphate-free composition is obtainable by mixing:
one or more water glass solutions each containing a silicate of the general empirical formula M 2 O·nSiO 2 , wherein “n” is a positive number of at least 2.5, but no greater than 4.5, and “M” is selected from sodium or potassium; with
the at least one water-insoluble oxide pigment C).

4. The method according to claim 1 , wherein component C) is selected from the water-insoluble oxide pigments of the elements Mg, Al, Mn, Zn, Ti and/or Zr.

5. The method according to claim 4 , wherein the aqueous chromium- and phosphate-free composition comprises:
A) at least 15 wt. %, but no more than 40 wt. %, of silicates dissolved in water, calculated as SiO 2 ;
B) at least 4 wt. %, but no more than 15 wt. %, of sodium and/or potassium ions dissolved in water, calculated as Na and/or K, respectively; and
C) at least 1 wt. %, but no more than 10 wt. %, of the at least one water-insoluble oxide pigment; and
component C) is selected from the water-insoluble oxide pigments of the elements Al, Ti and/or Zr.

6. The method according to claim 5 , wherein component C) is selected from the water-insoluble oxide pigments of the element Ti and the element Al, present in an amount ratio by mass Ti:Al in a range of from 70:30 to 30:70.

7. The method according to claim 1 , wherein amounts of organic compounds having a boiling point of less than 150° C. at 1 atm in the aqueous chromium- and phosphate-free composition are below 4 wt. %.

8. The method according to claim 1 , wherein amounts of organic compounds having a boiling point of less than 150° C. at 1 atm in the aqueous chromium- and phosphate-free composition are below 0.1 wt. %.

9. The method according to claim 1 , wherein Total Organic Content (TOC) includes all organic compounds containing C, and the TOC proportion in the aqueous chromium- and phosphate-free composition, calculated as CO 2 , is less than 10 g/kg.

10. The method according to claim 1 , wherein the wet film is dried by supplying heat such that a peak metal temperature of at least 200° C., but no more than 500° C., is maintained for a period of 1 to 200 seconds.

11. The method according to claim 10 , wherein the wet film is dried by supplying heat such that the peak metal temperature of 250° C.-400° C. is reached.

12. The method according to claim 1 , wherein such an amount of the wet film is applied that, after drying, a dry film layer thickness of at least 0.5 μm but no more than 5 μm is achieved.

13. The method according to claim 1 , wherein the electrical steel strip is made of steel comprising silicon in a range of 0.2-4.5 wt. %, and less than 0.05 wt. % carbon.

14. The method according to claim 1 , wherein the electrical steel strip is non-grain-oriented.

15. An aqueous dispersion, containing
A) at least 15 wt. %, but no more than 40 wt. %, of silicates dissolved in water, calculated as SiO 2 ;
B) at least 4 wt. %, but no more than 15 wt. %, of sodium and/or potassium ions dissolved in water, calculated as Na;
C) in total at least 1 wt. %, but in total no more than 10 wt. %, of water-insoluble oxide pigments, comprising oxide pigments of the element Ti and the element Al;
D) less than 10 mg/kg of phosphates, calculated as PO 4 ;
E) a Total Organic Content of less than 10 g/kg, calculated as the amount of CO 2 ;
obtainable by mixing one or more water glass solutions, each containing a silicate of the general empirical formula M 2 O·nSiO 2 , where n is a natural number of at least 2.5, but no greater than 4.5, and M is selected from sodium or potassium, with a corresponding amount of the water-insoluble oxide pigments.

16. A laminated electrical steel strip, comprising a plurality of electrical steel strip portions which are arranged one above the other, are welded to one another, and are provided with a coating consisting of silicate and oxide pigments of the elements Ti and Al, coated according to the method of claim 5 .

17. The method of claim 1 , wherein the at least one water-insoluble oxide pigment C) comprises at least one water insoluble-oxide pigment of the element Ti having an average particle size of 0.5 μm.

18. The method of claim 12 , wherein such an amount of the wet film is applied that, after drying, a dry film layer of at least 0.5 μm but no more than 2 μm is achieved.

19. The method of claim 1 , wherein the applied wet film layer has a thickness between 0.5 μm and 1.4 μm.

20. A method for coating an electrical steel strip, comprising steps of:
applying a wet film of an aqueous chromium- and phosphate-free composition to at least a part of a surface of the electrical steel strip, which composition comprises one or more water glass solutions, each containing a silicate of the general empirical formula M 2 O·nSiO 2 , where n is a natural number of at least 2.5, but no greater than 4.5, and M is selected from sodium or potassium; the one or more water glass solutions comprising:
A) at least 15 wt. %, but no more than 40 wt. %, of silicates dissolved in water, calculated as SiO 2 ; and
B) at least 4 wt. %, but no more than 15 wt. %, of sodium and/or potassium ions dissolved in water, calculated as Na and/or K;
the wet film further comprising
C) in total at least 1 wt. %, but no more than 10 wt. %, of water-insoluble oxide pigments, different from A) and B), selected from water-insoluble oxide pigments of the elements Mg, Al, Mn, Zn, Ti and/or Zr; and optionally further comprising water-insoluble oxide pigments of Ca and Si; and

drying the wet film on the surface of the electrical steel strip.

Assignees

• Henkel Ag & Co Kgaa

Inventors

• De Zeeuw Ard
• Bryden Todd
• Arnold Andreas
• Oliva Ramona
• Geick Volker

Classifications

• C09D1/02 Primary

  alkali metal silicates · CPC title

• H01F1/18

  with insulating coating · CPC title

• C09D5/08 Primary

  Anti-corrosive paints · CPC title

• C08K3/22

  of metals · CPC title

• C08K2003/2227

  of aluminium · CPC title